It was meant to be her big comeback following her kidney transplant, but Selena Gomez's American Music Awards performance has left some viewers underwhelmed.

The 25-year-old singer, who recently began dating ex Justin Bieber again, was accused of lip syncing after taking the stage to perform her new single 'Wolves' with Marshmello.

Image: Getty

"I love Selena Gomez but she made it so obvious that she lip synced through that whole performance hence why she had her head down and hair covering her face for 99 per cent of the performance," one person tweeted.

The pop superstar has been keeping a fairly low profile since stepping away from the spotlight to focus on her physical recovery after getting a kidney transplant from her friend Francia Raisa earlier this year due to her lupus struggle.

Many also took aim at her emotionally-charged theatrics, which began with Gomez -- who was dressed in a white slip dress and had fake blood on her knees -- being "kidnapped" by a troupe of all-female dancers.

But loyal Selenators have fiercely defended the singer, due to a rumour that Gomez had a panic attack before or during the performance.

"Some people should actually read before they comment," one fan tweeted. "Selena Gomez had a panic attack pre performance because she thought her singing wouldn't be good enough hence the lip syncing."

They added: "Now leave her the f--- alone."

DJ/producer Marshmello, who collaborated with Gomez on the 'Wolves' track, also stuck up for his friend.

"I honestly couldn’t be any more happy while watching @selenagomez deliver that performance," he wrote on Twitter. "Her talent is unreal, blessed to call her my friend."

Fan account Selena Gomez News was the first to tweet that the Texas-born entertainer had allegedly had an anxiety attack, however, neither Gomez nor her reps have confirmed the incident.

The hitmaker appeared to be in high spirits following her performance, sharing a clip of herself thanking her fans, and her "best friend Petra [Collins] for helping me bring it to life."